Mitigating electrode erosion in high temperature PEM fuel cell

Abstract

A method of operating a fuel cell power plant ( 10 ) including a stack ( 11 ) of fuel cells having an anode catalyst layer and a cathode electrode ( 15 ) including a catalyst layer disposed on catalyst support material is characterized by, during normal operation of said power plant, adjusting the voltage of the stack to be substantially equal to or less than a predetermined maximum voltage for the temperature of the stack. Further, said step of adjusting comprises adjusting the stack voltage to the lesser of: a) a predetermined voltage above which corrosion of catalyst support material is significant and below which corrosion of catalyst support material is insignificant at the temperature of the stack; and b) a predetermined voltage above which dissolution of catalyst is significant and below which dissolution of the catalyst is insignificant at the temperature of the stack.

The invention claimed is: 
     
       1. A method of operating a fuel cell power plant including a stack of fuel cells having an electric output and coolant passages having inlets and outlets, each fuel cell comprising an electrolyte disposed between an anode catalyst layer and a cathode including a catalyst layer disposed on catalyst support material, an anode fuel flow field plate on the anode side of the electrolyte and a cathode air flow field plate on the cathode side of the electrolyte, the power plant also having:
 a stack voltage sensor, 
 a stack temperature sensor, 
 a source providing hydrogen-containing fuel to the anode flow field plates, 
 an oxidant source providing oxidant to the cathode flow field plates, 
 a power conditioner connected between the electric output and a load, 
 a power plant controller; and 
 wherein said method comprises: 
 during normal operation of said power plant, adjusting the voltage of the stack to the lesser of: 
 a) a predetermined voltage above which corrosion of catalyst support material is significant at the temperature of the stack and below which corrosion of a catalyst support material is insignificant at the temperature of the stack; and 
 b) a predetermined voltage above which dissolution of catalyst is significant at the temperature of the stack and below which dissolution of the catalyst is insignificant at the temperature of the stack. 
 
     
     
       2. The method according to  claim 1  wherein adjusting the voltage of the stack comprises adjusting the stack voltage to be substantially equal to or less than a predetermined voltage above which erosion of an electrode is significant at the temperature of the stack and below which erosion of the electrode is insignificant at the temperature of the stack. 
     
     
       3. The method according to  claim 1  wherein adjusting the voltage of the stack comprises adjusting the electrical load on the stack. 
     
     
       4. The method according to  claim 3  wherein the power plant controller responds to the stack temperature sensor to regulate the load to cause the voltage of the stack indicated by the stack voltage sensor to be substantially equal to or less than the predetermined voltage. 
     
     
       5. The method according to  claim 1  wherein adjusting the voltage of the stack comprises adjusting current flow through an auxiliary load. 
     
     
       6. The method according to  claim 1  wherein adjusting the voltage of the stack comprises adjusting the current flow through a variable resistance. 
     
     
       7. The method according to  claim 1  wherein adjusting the voltage of the stack comprises adjusting current flow into an electric storage device. 
     
     
       8. The method according to  claim 1  wherein the oxidant source is controllable; and wherein adjusting the voltage of the stack comprises regulating the oxidant flow to the cathode flow field to control the voltage of the stack. 
     
     
       9. The method according to  claim 8  wherein the power plant controller responds to the stack temperature sensor to regulate oxidant flow to cause the voltage of the stack indicated by the stack voltage sensor to be substantially equal to or less than the predetermined voltage. 
     
     
       10. The method according to  claim 1  wherein the power conditioner is connected between the electric output and the load; and wherein adjusting the voltage of the stack comprises operating the power conditioner so as to adjust the load on the stack. 
     
     
       11. The method according to  claim 2  wherein the predetermined voltage above which erosion of an electrode is significant at the temperature of the stack and below which erosion of the electrode is insignificant at the temperature of the stack is less than or equal to 0.85 volts with respect to a hydrogen reference electrode when the temperature of the stack is 100 degrees Celsius. 
     
     
       12. The method according to  claim 11  wherein the electrode includes a noble metal catalyst and a carbon support. 
     
     
       13. The method according to  claim 2  wherein the predetermined voltage above which erosion of an electrode is significant at the temperature of the stack and below which erosion of the electrode is insignificant at the temperature of the stack is greater than or equal to 0.85 volts with respect to a hydrogen reference electrode when the temperature of the stack is 65 degrees Celsius. 
     
     
       14. The method according to  claim 13  wherein the electrode includes a noble metal catalyst and a carbon support.